1. Technical Field
This invention relates to an apparatus for vulcanizing pneumatic tires and particularly to a vulcanizing apparatus of a type having no vent holes in the mold.
2. Background Art
As for apparatus for vulcanizing pneumatic tires, there is known a vulcanizing machine of the two-piece mold type wherein the mold comprises an upper mold section for molding one side of the carcass and one half of the tread of a pneumatic tire and a lower mold section for molding the other side of the carcass and the remaining half of the tread, the upper mold section being vertically movable with respect to the lower mold section. A vulcanizing machine of the segmental mold type is also known wherein the mold comprises an upper mold section for molding one side of the carcass of a pneumatic tire, a lower mold section for molding the other side of the carcass, and a sector segment in the form of a segment for molding the tread, the upper mold section being vertically movable with respect to the lower mold section, said sector segment being slidable radially of the upper mold section, said sector segment being slid by the upward and downward movement of a jacket ring which surrounds said sector segment, said jacket ring having a downwardly diverging taper.
Thus, when the mold is closed, the air between the inner surface of the mold and the green tire surface is removed by suction to cause the green tire surface to contact the inner surface of the mold, thereby making it unnecessary to form vent holes. Such vulcanizing machine is known; for example, Japanese Patent Application Disclosure No. 26872/1973 discloses a system wherein a cylindrical hollow upper frame installed above the center of the upper mold section of the two-piece mold type for vertically moving said upper mold section has a doughnut-like upper platen fixed at the lower end thereof and a bell-shaped cover covering the upper mold fixed on the lower surface thereof, the upper end of said cover being fixed, while a cylindrical cover having the same diameter as the lower half of said bell-shaped cover is fixed upright on a lower platen supporting, from below, the lower mold section of the two-piece mold type, the arrangement being such that when the lowering movement of the upper mold section causes the lower edge of the bell-shaped cover and the upper edge of the cylindrical cover to approach each other with a predetermined distance therebetween and before the green tire contacts the mold and before the mold is closed, the lower end of a metal bellows fixed in advance to the bell-shaped cover is pressed at its lower end against the upper surface of the lower platen, or a cylindrical body fixed in place of the metal bellows is inserted in a labyrinth rubber packing on the lower platen, or the lower edge of the bell-shaped cover is pressed against a rubber tube fixed in advance to the upper edge of the cylindrical cover, whereby the space in the cover is closed, so that the air in said space in the cover is removed by suction through an exhaust tube connected to the top of the bell-shaped cover.
However, in the vulcanizing apparatus described above, since the bell-shaped cover covering the upper platen is fixed to the upper frame extending upward from the middle of the upper platen, the space requiring closing between the upper surface of the green tire and said cover is of substantial volume, and a long time is expended in removing the air therein by suction. Further, in the case where a metal bellows is used for closing, its diameter is greater than that of the bell-shaped cover and the pressure differential between the exterior and interior of the bellows is high, making it difficult to keep the spring characteristics uniform; thus, the parallelism of the lower surface of the bellows with the surface of the lower platen is decreased to make the airtight sealing insufficient. Further, in the case where a labyrinth rubber packing is used, the sealing quality deteriorates even if there is a slight misregistration between the cylindrical body fixed to the outer surface of the bell-shaped cover and the labyrinth rubber packing fixed to the lower platen. Further, in the case of using rubber, the rubber tube, when filled with air, is inflated to have a circular cross section. Therefore, in order to increase the lowering stroke of said bell-shaped cover which lasts from the time the lower edge of the bell-shaped cover starts to contact the upper surface of the rubber tube until the mold is closed, it is necessary to increase the diameter of the rubber tube, in which case there is a problem that the outer diameter of the apparatus must be increased.